The lasing action of a laser apparatus is normally terminated when;
1. The specific laser application requirements are satisfied;
2. The upper laser level is depleted; or
3. The lower laser level becomes so highly populated that the population inversion necessary for lasing is lost.
While the laser termination of item 1 above is by design, the latter two represent fundamental limitations on laser performance. The third condition for laser termination described above is referred to as lower laser level bottlenecking.
The undesirable bottlenecking condition is generally minimized by using laser compositions, pressures and temperatures which maximize the collisional relaxation of the population from the lower laser level, while minimizing the collisional relaxation of the population from the upper laser level.